Nonwoven fabric

Abstract

Provided is a nonwoven fabric having both excellent flexibility and processability to a product. This nonwoven fabric comprises heat bonding composite fibers with heat bonded intersections, wherein the specific volume of the nonwoven fabric is 140-200 cm3 / g, and the fiber density ratio between a high density part and a low density part in the nonwoven fabric is 1.5-2.0.

Description

nonwoven fabric

[0001] The present invention relates to a nonwoven fabric that is soft and has excellent processability into products.

[0002] Nonwoven fabrics used in applications that come into contact with human skin, such as hygiene products, are required to be more comfortable, specifically, to have excellent bulk and flexibility, and to have minimal roughness when rubbed against the skin.

[0003] For such applications, through-air nonwoven fabrics are often used. Through-air nonwoven fabrics are obtained by forming a web from composite fibers composed of at least two types of thermoplastic resins with different melting points and then heat-treating the web to thermally bond the intersections of the composite fibers. To heat-treat the web, a hot air penetration type heat treatment machine or a hot air blowing type heat treatment machine is used. However, blowing hot air exerts wind pressure on the web, which can cause problems such as loss of bulk and flexibility.

[0004] In view of these problems, the present applicant previously proposed that a bulky, flexible, and high-strength nonwoven fabric can be obtained by thermally bonding the intersections of thermally bondable conjugate fibers under no pressure using superheated steam gas (Patent Document 1). However, although the nonwoven fabric obtained in this manner is very bulky, there is room for improvement in terms of processability into products such as sanitary materials, such as ease of width adjustment and meandering.

[0005] International Publication No. 2022 / 202142

[0006] The present invention has been made against the background of the above-mentioned conventional technology, and an object of the present invention is to provide a nonwoven fabric that combines excellent softness with ease of processability into products.

[0007] The present inventors have conducted extensive research to solve the above-mentioned problems, and as a result have found that a nonwoven fabric that is bulky and has excellent flexibility, as well as excellent processability into products, can be obtained by adjusting the specific volume of the nonwoven fabric and the fiber density ratio between the high-density portion and the low-density portion of the nonwoven fabric within specific ranges, respectively, and have completed the present invention.

[0008] That is, the present invention has the following features: [1] A nonwoven fabric containing thermally bondable composite fibers whose intersections are thermally bonded, wherein the specific volume of the nonwoven fabric is 140 to 200 cm ３ / g, and the fiber density ratio between the high density region and the low density region in the nonwoven fabric is 1.5 to 2.0. [2] The nonwoven fabric according to [1], wherein the fineness of the thermal adhesive conjugate fiber is 0.3 to 20 dtex. [3] The nonwoven fabric according to [1] or [2], wherein the thermoplastic resin constituting the thermal adhesive conjugate fiber is at least one selected from polyethylene-based resins, polypropylene-based resins, and polyester-based resins. [4] The nonwoven fabric has a basis weight of 10 to 100 g / m ２ [5] A method for producing a nonwoven fabric, comprising: a step of obtaining a web containing thermally adhesive conjugate fibers; a heat treatment step A of thermally bonding the intersections of the thermally adhesive conjugate fibers under no pressure; and a heat treatment step B of blowing a heat medium onto the intermediate obtained in the heat treatment step A at an air speed of 1.5 m / sec or more. [6] A method for producing a nonwoven fabric according to [5], wherein the temperature of the heat medium in the heat treatment step B is −20 to +50°C lower than the melting point or softening point of the low-melting point component constituting the thermally adhesive conjugate fibers.

[0009] According to the present invention, a nonwoven fabric can be provided that has both excellent flexibility and ease of processability into products.

[0010] In the nonwoven fabric of this embodiment, the intersections of the thermally adhesive composite fibers are thermally bonded, the fiber density ratio between the high density portion and the low density portion in the nonwoven fabric is 1.5 to 2.0, and the specific volume is 140 to 200 cm ３ / g.

[0011] (Thermal adhesive conjugate fiber) The thermal adhesive conjugate fiber used in the nonwoven fabric of the present invention is not particularly limited as long as it can be melted by heat to form adhesive points, and its conjugate form can be exemplified by concentric sheath-core conjugate fiber, eccentric sheath-core conjugate fiber, or side-by-side conjugate fiber. In addition, the cross-sectional shape of the conjugate fiber is not particularly limited, and any of round shapes such as circle or ellipse, angular shapes such as triangle or square, irregular shapes such as star or octave, segmented shapes, and hollow shapes can be used.

[0012] The thermoplastic resin constituting the thermally bondable conjugate fiber in this embodiment is not particularly limited, and examples thereof include polyethylene-based resins such as low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), and high-density polyethylene (HDPE); polypropylene-based resins such as crystalline polypropylene (PP) and copolymers of propylene and α-olefins (excluding propylene) (Co-PP) containing propylene as the main component; polyester-based resins such as polyethylene terephthalate (PET), polybutylene terephthalate, copolymerized polyethylene terephthalate (Co-PET), polylactic acid, polyglycolic acid, and polybutylene succinate; polyvinyl alcohol-based resins, polyvinyl acetate-based resins, acrylic resins, polystyrene-based resins, polyurethane-based resins, polyamide-based resins, and fluorine-based resins. Among these, polyethylene-based resins, polypropylene-based resins, and polyester-based resins are preferred from the standpoints of moldability of the thermally bondable conjugate fiber and raw material costs. The combination of thermoplastic resins constituting the thermally adhesive conjugate fiber is not particularly limited, but from the viewpoint of widening the processing temperature range, the difference in melting point is preferably 10° C. or more, more preferably 30° C. or more, and even more preferably 50° C. or more. Specific examples of combinations of high-melting point component / low-melting point component of thermoplastic resins include PP / HDPE, PP / LLDPE, PP / Co-PP, PET / HDPE, PET / LLDPE, PET / Co-PET, and PET / PP. From the viewpoints of texture, raw material costs, production stability, etc., the combination of PP / HDPE or PET / HDPE is preferred, and the combination of PET / HDPE is more preferred.

[0013] The volume ratio of the low-melting point component to the high-melting point component in the thermal adhesive conjugate fiber is not particularly limited, but a large proportion of the low-melting point component tends to improve the adhesive strength between the thermal adhesive conjugate fibers and result in a nonwoven fabric with high tensile strength, while a large proportion of the high-melting point component tends to improve the texture of the nonwoven fabric or textile product. From this perspective, the volume ratio of the low-melting point component to the high-melting point component is preferably 20 / 80 to 80 / 20, and more preferably 30 / 70 to 70 / 30.

[0014] The thermoplastic resin constituting the thermal adhesive conjugate fiber may contain additives such as antioxidants, light stabilizers, ultraviolet absorbers, neutralizing agents, nucleating agents, epoxy stabilizers, lubricants, antibacterial agents, deodorizing agents, flame retardants, antistatic agents, pigments, or plasticizers, as needed, and these may be used in any combination, within the range that does not impair the effects of the present invention.

[0015] The fineness of the thermal adhesive conjugate fiber used in the nonwoven fabric of the present invention is not particularly limited, but is preferably 0.3 to 20 dtex, more preferably 0.5 to 10 dtex, and even more preferably 0.7 to 6.0 dtex. In particular, when used as a surface material for absorbent articles such as disposable diapers, the flexibility of the nonwoven fabric can be improved by using a thermal adhesive conjugate fiber with a low fineness.

[0016] The fiber length of the thermal adhesive conjugate fiber is not particularly limited, but is preferably 20 to 102 mm, more preferably 30 to 51 mm. In a web formation process such as by a carding method, a web excellent in openability and texture can be easily formed, and a nonwoven fabric having uniform physical properties can be obtained with a fiber length of 20 to 102 mm.

[0017] (Nonwoven Fabric) In the nonwoven fabric of the present invention, the intersections of the thermally adhesive composite fibers are thermally bonded, the fiber density ratio between the high density portion and the low density portion of the nonwoven fabric is 1.5 to 2.0, and the specific volume is 140 to 200 cm ３ / g. Conventionally, there has been a trade-off between flexibility and processability into products, and it has been difficult to achieve both. In the present invention, attention is focused on the relationship between the specific volume and fiber density ratio of a nonwoven fabric with respect to flexibility and processability into products, and it has been found that by setting a specific specific volume and fiber density ratio, the trade-off between flexibility and processability into products can be resolved.

[0018] Here, the terms "high-density region" and "low-density region" used in this specification refer to the upper and lower regions of the nonwoven fabric divided into three equal parts in the thickness direction, and the "high-density region" refers to the region with a higher fiber density when measuring the fiber density, and the "low-density region" refers to the region with a lower fiber density.

[0019] In addition, the term "fiber density" as used herein refers to the number of fibers per unit area in the cross section of the nonwoven fabric, and is expressed in units of, for example, fibers / mm２ The method for measuring the fiber density will be explained in detail in the Examples.

[0020] The fiber density ratio between the high-density region and the low-density region in the nonwoven fabric of the present invention is 1.5 to 2.0. A fiber density ratio of 1.5 or more can impart a certain degree of rigidity to the nonwoven fabric, improving processability into products, while a fiber density ratio of 2.0 or less can prevent the fibers from becoming excessively dense, improving the flexibility of the nonwoven fabric. From this perspective, the fiber density ratio is preferably 1.55 to 1.95, and more preferably 1.6 to 1.9.

[0021] The fiber density of the high-density portion of the nonwoven fabric of the present invention is not particularly limited, but is preferably 10.0 to 40.0 fibers / mm ２ It is preferable that the number of threads / mm is 15.0 to 35.0. ２ More preferably, the number of threads / mm is 20.0 to 30.0. ２ In order to obtain a nonwoven fabric with a sufficient number of fibers in contact with each other and good processability into products, the fiber density of the high density portion is 10.0 fibers / mm ２ In order to obtain a good texture of the nonwoven fabric, the fiber density of the high density portion is preferably 40.0 fibers / mm ２ The fiber density of the low density region should be within the range of the fiber density of the high density region and the range of the fiber density ratio between the high density region and the low density region, that is, 5.0 to 26.7 fibers / mm ２ is preferred.

[0022] The tensile strength per unit area weight of the nonwoven fabric of the present invention is not particularly limited, but in order to obtain a nonwoven fabric with good processability into products, it is preferably 1.25 N / 5 cm or more, more preferably 1.40 N / 5 cm or more, and even more preferably 1.50 N / 5 cm or more. Furthermore, the upper limit of the tensile strength per unit area weight is not particularly limited, but in consideration of the flexibility of the nonwoven fabric, it is preferably 2.50 N / 5 cm or less, and more preferably 1.80 N / 5 cm or less.

[0023] The 5% tensile strength of the nonwoven fabric of the present invention is not particularly limited, but in order to obtain a nonwoven fabric with good processability into products, it is preferably 0.8 N / 5 cm or more, more preferably 1.3 N / 5 cm or more, and even more preferably 1.8 N / 5 cm or more.

[0024] The processability into products is evaluated in a comprehensive manner using the indices of tensile strength per unit area weight and 5% tensile strength of the nonwoven fabric.

[0025] The specific volume of the nonwoven fabric of the present invention is 140 to 200 cm ３ / g. The specific volume is 140 cm ３ / g or more, the nonwoven fabric is bulky and has good flexibility, and ３ / g or less, the number of bonding points of the fibers is sufficient, and the processability into products is good. ３ / g, and 160 to 180 cm ３ / g is more preferable.

[0026] The basis weight of the nonwoven fabric of the present invention is not particularly limited, but is preferably 10 to 100 g / m ２ It is preferable that the density is 15 to 70 g / m ２ It is more preferable that the thickness is 10 g / m in order to improve the processability into products. ２ More than 100 g / m is preferable, and 100 g / m is preferable for good flexibility. ２ In particular, when used as a surface material for absorbent articles such as diapers, the preferred weight is 15 to 40 g / m ２ It is more preferable that:

[0027] The compression work (WC) of the nonwoven fabric of the present invention is not particularly limited, but is preferably 4.0 gf cm / cm ２ It is preferable that the viscosity is 4.1 gf cm / cm or more. ２ More preferably, it is 4.2 gf cm / cm or more. ２ The compression work load is a measure of the softness of a nonwoven fabric, and the greater the compression work load, the better the softness can be evaluated. The method for measuring the compression work load will be described in detail in the Examples.

[0028] In addition to the thermally bondable composite fibers described above, the nonwoven fabric of the present invention may contain fibers that do not have thermal bonding properties (hereinafter referred to as "non-thermally bondable fibers"), such as natural fibers (e.g., wood fibers), regenerated fibers (e.g., rayon), semi-synthetic fibers (e.g., acetate), chemical fibers, and synthetic fibers (e.g., polyester fibers, acrylic fibers, nylon fibers, and vinyl chloride fibers). "Non-thermally bondable fibers" refer to fibers that do not undergo thermal changes (melting or softening) that contribute to thermal bonding during the heat treatment process used to produce the nonwoven fabric. When non-thermally bondable fibers are included, the proportion of the non-thermally bondable fibers relative to the total weight of the nonwoven fabric is not limited as long as it does not impair the effects of the present invention, but can be, for example, 1 to 30 wt%, preferably 3 to 15 wt%. To achieve effects commensurate with the intended use, the proportion of non-thermally bondable fibers is preferably 1 wt% or more, and preferably 30 wt% or less, to obtain a nonwoven fabric that is less likely to fluff.

[0029] The nonwoven fabric of the present invention may be a single-layer nonwoven fabric, or may be a multi-layer nonwoven fabric having different finenesses, compositions, or densities. In the case of a multi-layer nonwoven fabric, for example, by laminating layers of different finenesses, the size of the gaps formed between the fibers can be varied in the thickness direction of the nonwoven fabric, thereby controlling the flexibility and processability. The method for producing a multi-layer nonwoven fabric is not particularly limited, but an example is a method in which webs containing thermally adhesive composite fibers having different finenesses, compositions, densities, etc. are overlapped and thermally adhesively treated.

[0030] The nonwoven fabrics of the present invention may also be laminated together. For example, when two types of nonwoven fabrics are laminated together, the first layer and the second layer each have a "low-density region" and a "high-density region." The low-density region of the first layer may be adjacent to the high-density region of the second layer, or the high-density region of the first layer may be adjacent to the low-density region of the second layer, or the high-density region of the first layer may be adjacent to the low-density region of the second layer, or the high-density region of the first layer may be adjacent to the low-density region of the second layer. The method for laminating the nonwoven fabrics is not particularly limited, but examples include a method of laminating the nonwoven fabrics using an adhesive such as a hot melt, or a method of thermal bonding using through-air, hot embossing, ultrasonic processing, or the like.

[0031] Furthermore, the nonwoven fabric of the present invention may be laminated with a nonwoven fabric, film, or sheet other than the nonwoven fabric of the present invention, such as, but not limited to, a through-air nonwoven fabric, a spunbond nonwoven fabric, a meltblown nonwoven fabric, a spunlace nonwoven fabric, a needle-punched nonwoven fabric, a film, a mesh, or a net. By laminating, it is possible to control liquid permeability, liquid permeation rate, liquid return, processability into products, etc. The method of laminating can be, but is not limited to, a method of laminating with an adhesive such as a hot melt, or a method of laminating with thermal bonding such as through-air, hot embossing, or ultrasonic processing.

[0032] The nonwoven fabric of the present invention may be subjected to antistatic treatment, water-repellent treatment, hydrophilic treatment, antibacterial treatment, ultraviolet absorbing treatment, near-infrared absorbing treatment, electret treatment, or the like depending on the purpose, as long as the effects of the present invention are not impaired.

[0033] (Method for producing nonwoven fabric) The method for producing a nonwoven fabric of the present invention includes a step of obtaining a web containing thermally bondable conjugate fibers, a heat treatment step A in which the intersections of the thermally bondable conjugate fibers are thermally bonded without pressure, and a heat treatment step B in which a heat medium is blown onto the intermediate obtained in the heat treatment step A at an air speed of 1.5 m / sec or more. The intermediate obtained in the heat treatment step A is heat-treated without pressure, so that it has a low fiber density ratio in the thickness direction, is bulky, and has excellent flexibility, but is poor in processability into products. In the heat treatment step B, by blowing a heat medium onto the intermediate at a specific air speed, it is possible to adjust the fiber density ratio between the high-density and low-density regions of the nonwoven fabric and impart processability to the product. Furthermore, because the fibers are fixed to a certain extent by the heat treatment step A, it is believed that the bulk is not lost and flexibility can be maintained.

[0034] The web containing the thermally adhesive conjugate fiber is not particularly limited, and may be a long-fiber web formed by a spunbonding method, a meltblown method, a tow-spreading method, or the like, or a short-fiber web formed by a carding method, an airlaid method, a wet method, or the like using short fibers (staples or chopped fibers). Of these, from the viewpoint of improving the specific volume, a web formed by a carding method or an airlaid method is preferred, and a web formed by a carding method is more preferred. In the present invention, the term "web" refers to a fiber assembly in which the fibers are somewhat entangled, and means a state in which the intersections of the thermally adhesive conjugate fibers are not bonded.

[0035] Next, in the heat treatment step A, the intersections of the heat-bondable composite fibers in the obtained web are heat-bonded without pressure to obtain an intermediate. The heat medium in the heat treatment step A is not particularly limited, and examples include hot air, far infrared rays, and superheated steam gas. However, superheated steam gas is preferably used in terms of productivity, excellent texture, and reduced fuzzing. Examples of the heat treatment step A include a method in which a heat medium is blown onto at least one of the top and bottom surfaces of the web at a wind speed of preferably 0.5 m / sec or less, more preferably 0.2 m / sec or less, even more preferably 0.1 m / sec or less, and particularly preferably less than 0.1 m / sec, or a method in which the web is introduced into a (non-winding) oven filled with a heat medium. The heat treatment may be carried out without pressure, and may be carried out at atmospheric pressure, low pressure, or vacuum. However, from the viewpoint of simplifying the equipment, atmospheric pressure is preferred. The heat treatment step is preferably carried out by introducing the web into a furnace using a transport conveyor or the like to continuously obtain a nonwoven fabric.

[0036] The temperature of the heat medium in the heat treatment step A is not particularly limited, but is preferably at least +0°C above the melting point or softening point of the low-melting point component constituting the thermally adhesive conjugate fiber and not more than -0°C above the melting point or softening point of the high-melting point component. When the temperature of the heat medium is at least +0°C above the melting point or softening point of the low-melting point component, the intersections of the thermally adhesive conjugate fibers can be bonded, while when the temperature is not more than -0°C above the melting point or softening point of the high-melting point component, an intermediate can be obtained without melting or softening the high-melting point component. From this perspective, the temperature is preferably at least +10°C above the melting point or softening point of the low-melting point component constituting the thermally adhesive conjugate fiber and not more than -10°C above the melting point or softening point of the high-melting point component, and more preferably at least +20°C above the melting point or softening point of the low-melting point component and not more than -20°C above the melting point or softening point of the high-melting point component.

[0037] The heat medium blowing speed in the heat treatment step A is not particularly limited as long as it is within a range where no pressure reduction occurs, but is preferably 0.5 m / sec or less, more preferably 0.3 m / sec or less, even more preferably 0.1 m / sec or less, and particularly preferably less than 0.1 m / sec. The heat medium blowing pressure is not particularly limited as long as it is within a range where no pressure reduction occurs, but is preferably less than 0.1 kPaG.

[0038] The treatment time of the heat treatment step A is not particularly limited, but is preferably 60 seconds or less, and more preferably 30 seconds or less. In order to produce with satisfactory productivity, the treatment time is preferably 60 seconds or less.

[0039] A nonwoven fabric is obtained by further blowing a heat medium onto the intermediate product that has undergone the heat treatment step A in the heat treatment step B. The heat treatment method is not particularly limited, and examples thereof include a through-air treatment in which circulating hot air is applied to the nonwoven fabric, and a floating dryer treatment in which hot air is applied from above and below the nonwoven fabric while the nonwoven fabric is floating.

[0040] The temperature of the heat medium in the heat treatment step B in the present invention is not particularly limited, but is preferably −20 to +50°C the melting point or softening point of the low-melting point component constituting the thermally adhesive composite fiber. A temperature of −20°C or higher than the melting point or softening point of the low-melting point component constituting the thermally adhesive composite fiber is preferred because spraying the heat medium makes it easier to keep the fiber density within a specific range, while a temperature of +50°C or lower is preferred because spraying the heat medium can prevent a significant reduction in thickness. From this perspective, the temperature of the heat medium in the heat treatment step B is preferably −10 to +40°C the melting point or softening point of the low-melting point component, more preferably +0°C to +30°C. For a combination of PET / HDPE, a temperature of 110 to 180°C is an example.

[0041] The air speed of the heat medium in the heat treatment step B in the present invention is 1.5 m / sec or more. When the air speed of the heat medium in the heat treatment step B is 1.5 m / sec or more, the fiber density ratio can be set within a specific range, the nonwoven fabric has a certain degree of rigidity, and processing into products becomes good. From this viewpoint, 1.8 m / sec or more is preferable, and 2.0 m / sec or more is more preferable. Furthermore, the upper limit of the air speed of the heat medium in the heat treatment step B is not particularly limited, but from the viewpoint of maintaining the texture of the nonwoven fabric, it is preferably 4.0 m / sec or less, more preferably 3.5 m / sec or less, and even more preferably 3.0 m / sec or less.

[0042] The treatment time of the heat treatment step B is not particularly limited, but is preferably 60 seconds or less, and more preferably 30 seconds or less. In order to produce with satisfactory productivity, the treatment time is preferably 60 seconds or less.

[0043] The nonwoven fabric of the present invention can be used for, for example, absorbent articles such as diapers, napkins, and incontinence pads; sanitary materials such as masks, gowns, surgical gowns, and bandages; interior materials such as wall sheets, shoji paper, and flooring; daily life materials such as cover cloths, cleaning wipers, and food waste covers; toiletry products such as disposable toilets and toilet covers; pet supplies such as pet sheets, pet diapers, and pet towels; industrial materials such as wiping materials, filters, cushioning materials, oil adsorbents, abrasives, and adsorbents for ink tanks; and textile products such as general medical materials, bedding, and nursing care products.

[0044] The present invention will be described in detail below with reference to examples, but the present invention is not limited thereto. The measurement methods or definitions of the physical properties shown in the examples are as follows. All of the following physical property measurements were carried out after the nonwoven fabric was heat-treated in an oven at 110°C for 5 minutes to reset the stress of the nonwoven fabric.

[0045] <Fineness of Thermally Bondable Conjugate Fiber> The fineness of the thermally bondable conjugate fiber was measured in accordance with JIS L 1015 using a single yarn physical property measuring device (FAVIMAT) manufactured by Textechno Co., Ltd. The fineness was taken as the average value of 50 fibers.

[0046] <Fiber Density of High-Density Portions and Low-Density Portions> (1) Method for Preparing Observation Samples A nonwoven fabric sample was cut into a 1 cm (machine direction of the nonwoven fabric; MD) x 2 cm (width direction of the nonwoven fabric; CD) piece. The nonwoven fabric was thoroughly impregnated with a photocurable resin (UV-LED Resin Hoshi no Shizuku [Soft] manufactured by PADICO Corporation (Hoshi no Shizuku is a registered trademark)) and cured by UV irradiation. Next, using a microtome (RM2265 manufactured by Leica Corporation), the cured sample was cut to a thickness of 10 μm in the MD, obtaining a 10 μm (MD) x 2 cm (CD) sample for observation. (2) Measurement of fiber density Using a microscope (VHX-6000 manufactured by KEYENCE Corporation) and a polarizing plate, the microtome cut surface of the observation sample was observed at 20 to 50 magnifications, and the number of fibers per area was measured (number of fibers / mm ) at each of the upper and lower parts of the cut surface, which were divided into three equal parts in the thickness direction. ２ The larger value was taken as the fiber density of the high density region, and the smaller value was taken as the fiber density of the low density region. Each fiber density was measured twice and the average value was taken as the fiber density.

[0047] <Fiber density ratio between high-density portion and low-density portion> Using the values ​​of the fiber density of the high-density portion and the fiber density of the low-density portion obtained by the above method, the fiber density ratio between the high-density portion and the low-density portion was calculated according to the following formula: Fiber density ratio between high-density portion and low-density portion = Fiber density of high-density portion (strands / mm ２ ) ÷ fiber density of low density area (fibers / mm ２ )

[0048] <Basis Weight> The weight of a nonwoven fabric cut into a 100 mm x 100 mm piece was measured, and the value converted to a unit area was used as the basis weight (g / m ２ The basis weight was calculated as the average value of two measurements.

[0049] <Tensile strength> A sample measuring 50 mm x 150 mm was cut out in the machine direction and pulled using an autograph (AGX-J) manufactured by Shimadzu Corporation at a chuck distance of 100 mm and a pulling speed of 100 mm / min. The maximum strength measured was taken as the tensile strength of the nonwoven fabric. The tensile strength was measured three times and the average value was used.

[0050] <Tensile strength per unit basis weight> The tensile strength of the nonwoven fabric is expressed as a unit basis weight (g / m ２ The value obtained by dividing the tensile strength by the tensile strength per unit area weight of the nonwoven fabric was determined.

[0051] <5% Tensile Strength> A tensile test was performed in the same manner as in <Strength>, and the tensile load at a chuck distance of 105 mm (a state in which the specimen was stretched 5% from the 100 mm distance at the start of the tensile test) was defined as the 5% tensile strength. The 5% tensile strength was calculated as the average value of three measurements.

[0052] <Processability into Products> The processability into products was evaluated using the tensile strength per unit basis weight and the 5% tensile strength of the nonwoven fabric according to the following criteria: ◯: When the tensile strength per unit basis weight is 1.25 N / 5 cm or more and the 5% tensile strength is 0.8 N / 5 cm or more ◯: When either or both of the tensile strength per unit basis weight is 1.25 N / 5 cm or more and the 5% tensile strength is 0.8 N / 5 cm or more are not satisfied: ×

[0053] <Compression Work (WC)> Using a handy compressor (KES-G5, manufactured by Kato Tech Co., Ltd.), the compression work was measured as follows. First, a nonwoven fabric was placed on a sample stage, and a sample with an area of ​​2 cm ２ The pressure probe was applied from above the sample at a SENS (sensitivity): 2, a speed: 0.2 mm / sec, and a stress of 50 gf / cm ２ The specimen was compressed until the stress curve Pa against the distance was obtained. The compression work (WC) was calculated from the obtained Pa by numerical processing. The compression work was calculated as the average value of three measurements.

[0054] <Softness> The softness of the nonwoven fabric was evaluated according to the following criteria: WC of 4.0 or more: Good WC of less than 4.0: Bad

[0055] <Thickness> <Compression work (WC)> When measuring, the stress is 0.5 gf / cm ２ The thickness was measured at the time of application, and the average value of three measurements was used.

[0056] <Specific volume> The basis weight of the nonwoven fabric (g / m ２ The specific volume of the nonwoven fabric was calculated from the thickness (mm) and the specific volume (cm) of the nonwoven fabric using the following formula: ３ / g) = Thickness (mm) ÷ Basis weight (g / m ２ ) x 1000

[0057] [Example 1] A core is made of polyethylene terephthalate (intrinsic viscosity (measured using an equal weight mixed solvent of phenol and tetrachloroethane, concentration 0.5 g / 100 ml, temperature 20°C): 0.64 dl / g, melting point: 250°C), and a sheath is made of high-density polyethylene (density: 0.956 g / cm ３ A concentric sheath-core thermal adhesive composite fiber having a fineness of 1.7 dtex and a fiber length of 45 mm was prepared. The fiber had a melt flow rate (190°C, load 21.18N): 16.5 g / 10 min, and a melting point of 130°C) in a volume ratio of 50 / 50. A web containing the thermal adhesive composite fiber was produced by a carding method, and the web was introduced into a furnace filled with superheated steam gas at 180°C for 10 seconds to perform a heat treatment step A, thereby obtaining an intermediate. The wind speed of the superheated steam gas was less than 0.1 m / sec. Next, a nonwoven fabric was obtained by performing a heat treatment step B using a hot air circulation dryer with circulating hot air at 130°C and 2.1 m / sec for 10 seconds.

[0058] Example 2 A nonwoven fabric was obtained in the same manner as in Example 1, except that the wind speed of the circulating hot air in the heat treatment step B was set to 2.5 m / sec.

[0059] Example 3 A nonwoven fabric was obtained in the same manner as in Example 1, except that the wind speed of the circulating hot air in the heat treatment step B was set to 2.9 m / sec.

[0060] Comparative Example 1 A web obtained in the same manner as in Example 1 was introduced into a furnace filled with superheated steam gas at 180° C. for 10 seconds to obtain a nonwoven fabric.

[0061] Comparative Example 2 A nonwoven fabric was obtained in the same manner as in Example 1, except that the wind speed of the circulating hot air in the heat treatment step B was set to 0.8 m / sec.

[0062] Comparative Example 3 A nonwoven fabric was obtained in the same manner as in Example 1, except that the wind speed of the circulating hot air in the heat treatment step B was set to 1.3 m / sec.

[0063] Comparative Example 4 A web obtained in the same manner as in Example 1 was heat-treated in a hot air circulation dryer with circulating hot air at 130° C. and 1.3 m / sec to obtain a nonwoven fabric.

[0064] [Example 4] A core is made of polyethylene terephthalate (intrinsic viscosity (measured using an equal weight mixed solvent of phenol and tetrachloroethane, concentration 0.5 g / 100 ml, temperature 20°C): 0.64 dl / g, melting point: 250°C), and a sheath is made of high-density polyethylene (density: 0.956 g / cm ３ A concentric sheath-core type thermal adhesive composite fiber having a fineness of 4.4 dtex and a fiber length of 51 mm and a volume ratio of 50 / 50 was prepared. A web containing the thermal adhesive composite fiber was produced by a carding method, and the web was introduced into a furnace filled with superheated steam gas at 180°C for 10 seconds, thereby carrying out a heat treatment step A. The air velocity of the superheated steam gas was less than 0.1 m / sec. A nonwoven fabric was then obtained by a heat treatment step B using a hot air circulation dryer at 140°C and circulating hot air at 2.9 m / sec.

[0065] Comparative Example 5 A web obtained in the same manner as in Example 4 was introduced into a furnace filled with superheated steam gas at 180° C. for 10 seconds to obtain a nonwoven fabric.

[0066] Comparative Example 6 A web obtained in the same manner as in Example 4 was heat-treated with hot air at 130° C. and a circulating air speed of 1.3 m / sec in a hot air circulation dryer to obtain a nonwoven fabric.

[0067] The preparation conditions and physical properties of the nonwoven fabrics of Examples 1 to 3 are summarized in Table 1.

[0068]

[0069] The preparation conditions and physical properties of the nonwoven fabrics of Comparative Examples 1 to 3 are summarized in Table 2.

[0070]

[0071] The preparation conditions and physical properties of the nonwoven fabrics of Example 4 and Comparative Examples 5 and 6 are summarized in Table 3.

[0072]

[0073] As can be seen from Tables 1 to 3, the specific volume is 140 to 200 cm ３ The nonwoven fabrics of Examples 1 to 4, in which the fiber density ratio between the high density portion and the low density portion of the nonwoven fabric was 1.5 to 2.0, had both excellent flexibility and processability into products. In particular, a nonwoven fabric was obtained in Example 4 that had a high level of balance between flexibility and processability into products. On the other hand, ３ The nonwoven fabrics of Comparative Examples 1, 2, 3 and 5, in which the fiber density ratio between the high density region and the low density region was 1.5 or more, were excellent in softness, but the processability into products was impaired. ３ The nonwoven fabrics of Comparative Examples 4 and 6, in which the fiber density ratio between the high density portion and the low density portion was less than 2.0 / g and the fiber density ratio between the high density portion and the low density portion was more than 2.0, were excellent in processability into products, but the flexibility was significantly impaired.

[0074] The nonwoven fabric of the present invention is a nonwoven fabric excellent in flexibility and processability into products, and can be used for absorbent articles such as disposable diapers, sanitary napkins, and incontinence pads; sanitary materials such as masks, gowns, surgical gowns, and bandages; interior materials such as wall sheets, shoji paper, and flooring; daily life materials such as cover cloths, cleaning wipers, and food waste covers; toiletry products such as disposable toilets and toilet covers; pet supplies such as pet sheets, pet diapers, and pet towels; industrial materials such as wiping materials, filters, cushioning materials, oil adsorbents, abrasives, and adsorbents for ink tanks; and textile products such as general medical materials, bedding, and nursing care products.

Claims

1. A nonwoven fabric containing thermally bondable composite fibers whose intersections are thermally bonded, and the specific volume of the nonwoven fabric is 140 to 200 cm ３ / g, and the fiber density ratio of the high density region to the low density region in the nonwoven fabric is 1.5 to 2.

0.

2. The nonwoven fabric according to claim 1, wherein the fineness of the thermal adhesive composite fiber is 0.3 to 20 dtex.

3. The nonwoven fabric according to claim 1 or 2, wherein the thermoplastic resin constituting the thermally adhesive composite fiber is at least one selected from polyethylene-based resins, polypropylene-based resins, and polyester-based resins.

4. The nonwoven fabric has a basis weight of 10 to 100 g / m ２ The nonwoven fabric according to claim 1 or 2, 5. A method for producing a nonwoven fabric, comprising: a step of obtaining a web containing thermally adhesive composite fibers; a heat treatment step A of thermally bonding the intersections of the thermally adhesive composite fibers under no pressure; and a heat treatment step B of blowing a heat medium onto the intermediate obtained in the heat treatment step A at a wind speed of 1.5 m / sec or more.

6. The method for producing a nonwoven fabric according to claim 5, wherein the temperature of the heat medium in the heat treatment step B is −20 to +50° C. lower than the melting point or softening point of the low-melting point component constituting the thermally adhesive composite fiber.

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